1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1989, 1993, 1994 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * Routines to compress and uncompess tcp packets (for transmission 34 * over low speed serial lines. 35 * 36 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 37 * - Initial distribution. 38 * 39 */ 40 41 #include <sys/param.h> 42 #include <sys/mbuf.h> 43 #include <sys/systm.h> 44 45 #include <netinet/in.h> 46 #include <netinet/in_systm.h> 47 #include <netinet/ip.h> 48 #include <netinet/tcp.h> 49 50 #include <net/slcompress.h> 51 52 #ifndef SL_NO_STATS 53 #define INCR(counter) ++comp->counter; 54 #else 55 #define INCR(counter) 56 #endif 57 58 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n)) 59 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n)) 60 61 void 62 sl_compress_init(struct slcompress *comp, int max_state) 63 { 64 u_int i; 65 struct cstate *tstate = comp->tstate; 66 67 if (max_state == -1) { 68 max_state = MAX_STATES - 1; 69 bzero((char *)comp, sizeof(*comp)); 70 } else { 71 /* Don't reset statistics */ 72 bzero((char *)comp->tstate, sizeof(comp->tstate)); 73 bzero((char *)comp->rstate, sizeof(comp->rstate)); 74 } 75 for (i = max_state; i > 0; --i) { 76 tstate[i].cs_id = i; 77 tstate[i].cs_next = &tstate[i - 1]; 78 } 79 tstate[0].cs_next = &tstate[max_state]; 80 tstate[0].cs_id = 0; 81 comp->last_cs = &tstate[0]; 82 comp->last_recv = 255; 83 comp->last_xmit = 255; 84 comp->flags = SLF_TOSS; 85 } 86 87 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 88 * checks for zero (since zero has to be encoded in the long, 3 byte 89 * form). 90 */ 91 #define ENCODE(n) { \ 92 if ((u_int16_t)(n) >= 256) { \ 93 *cp++ = 0; \ 94 cp[1] = (n); \ 95 cp[0] = (n) >> 8; \ 96 cp += 2; \ 97 } else { \ 98 *cp++ = (n); \ 99 } \ 100 } 101 #define ENCODEZ(n) { \ 102 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 103 *cp++ = 0; \ 104 cp[1] = (n); \ 105 cp[0] = (n) >> 8; \ 106 cp += 2; \ 107 } else { \ 108 *cp++ = (n); \ 109 } \ 110 } 111 112 #define DECODEL(f) { \ 113 if (*cp == 0) {\ 114 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 115 cp += 3; \ 116 } else { \ 117 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 118 } \ 119 } 120 121 #define DECODES(f) { \ 122 if (*cp == 0) {\ 123 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 124 cp += 3; \ 125 } else { \ 126 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 127 } \ 128 } 129 130 #define DECODEU(f) { \ 131 if (*cp == 0) {\ 132 (f) = htons((cp[1] << 8) | cp[2]); \ 133 cp += 3; \ 134 } else { \ 135 (f) = htons((u_int32_t)*cp++); \ 136 } \ 137 } 138 139 /* 140 * Attempt to compress an outgoing TCP packet and return the type of 141 * the result. The caller must have already verified that the protocol 142 * is TCP. The first mbuf must contain the complete IP and TCP headers, 143 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the 144 * compression state, and "compress_cid" tells us whether it is OK 145 * to leave out the CID field when feasible. 146 * 147 * The caller is responsible for adjusting m->m_pkthdr.len upon return, 148 * if m is an M_PKTHDR mbuf. 149 */ 150 u_int 151 sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp, 152 int compress_cid) 153 { 154 struct cstate *cs = comp->last_cs->cs_next; 155 u_int hlen = ip->ip_hl; 156 struct tcphdr *oth; 157 struct tcphdr *th; 158 u_int deltaS, deltaA; 159 u_int changes = 0; 160 u_char new_seq[16]; 161 u_char *cp = new_seq; 162 163 /* 164 * Bail if this is an IP fragment or if the TCP packet isn't 165 * `compressible' (i.e., ACK isn't set or some other control bit is 166 * set). (We assume that the caller has already made sure the 167 * packet is IP proto TCP). 168 */ 169 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 170 return (TYPE_IP); 171 172 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 173 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 174 return (TYPE_IP); 175 /* 176 * Packet is compressible -- we're going to send either a 177 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 178 * to locate (or create) the connection state. Special case the 179 * most recently used connection since it's most likely to be used 180 * again & we don't have to do any reordering if it's used. 181 */ 182 INCR(sls_packets) 183 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 184 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 185 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 186 /* 187 * Wasn't the first -- search for it. 188 * 189 * States are kept in a circularly linked list with 190 * last_cs pointing to the end of the list. The 191 * list is kept in lru order by moving a state to the 192 * head of the list whenever it is referenced. Since 193 * the list is short and, empirically, the connection 194 * we want is almost always near the front, we locate 195 * states via linear search. If we don't find a state 196 * for the datagram, the oldest state is (re-)used. 197 */ 198 struct cstate *lcs; 199 struct cstate *lastcs = comp->last_cs; 200 201 do { 202 lcs = cs; cs = cs->cs_next; 203 INCR(sls_searches) 204 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 205 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 206 && *(int32_t *)th == 207 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 208 goto found; 209 } while (cs != lastcs); 210 211 /* 212 * Didn't find it -- re-use oldest cstate. Send an 213 * uncompressed packet that tells the other side what 214 * connection number we're using for this conversation. 215 * Note that since the state list is circular, the oldest 216 * state points to the newest and we only need to set 217 * last_cs to update the lru linkage. 218 */ 219 INCR(sls_misses) 220 comp->last_cs = lcs; 221 hlen += th->th_off; 222 hlen <<= 2; 223 if (hlen > m->m_len) 224 return TYPE_IP; 225 goto uncompressed; 226 227 found: 228 /* 229 * Found it -- move to the front on the connection list. 230 */ 231 if (cs == lastcs) 232 comp->last_cs = lcs; 233 else { 234 lcs->cs_next = cs->cs_next; 235 cs->cs_next = lastcs->cs_next; 236 lastcs->cs_next = cs; 237 } 238 } 239 240 /* 241 * Make sure that only what we expect to change changed. The first 242 * line of the `if' checks the IP protocol version, header length & 243 * type of service. The 2nd line checks the "Don't fragment" bit. 244 * The 3rd line checks the time-to-live and protocol (the protocol 245 * check is unnecessary but costless). The 4th line checks the TCP 246 * header length. The 5th line checks IP options, if any. The 6th 247 * line checks TCP options, if any. If any of these things are 248 * different between the previous & current datagram, we send the 249 * current datagram `uncompressed'. 250 */ 251 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 252 deltaS = hlen; 253 hlen += th->th_off; 254 hlen <<= 2; 255 if (hlen > m->m_len) 256 return TYPE_IP; 257 258 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 259 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 260 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 261 th->th_off != oth->th_off || 262 (deltaS > 5 && 263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 264 (th->th_off > 5 && 265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 266 goto uncompressed; 267 268 /* 269 * Figure out which of the changing fields changed. The 270 * receiver expects changes in the order: urgent, window, 271 * ack, seq (the order minimizes the number of temporaries 272 * needed in this section of code). 273 */ 274 if (th->th_flags & TH_URG) { 275 deltaS = ntohs(th->th_urp); 276 ENCODEZ(deltaS); 277 changes |= NEW_U; 278 } else if (th->th_urp != oth->th_urp) 279 /* argh! URG not set but urp changed -- a sensible 280 * implementation should never do this but RFC793 281 * doesn't prohibit the change so we have to deal 282 * with it. */ 283 goto uncompressed; 284 285 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 286 if (deltaS) { 287 ENCODE(deltaS); 288 changes |= NEW_W; 289 } 290 291 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 292 if (deltaA) { 293 if (deltaA > 0xffff) 294 goto uncompressed; 295 ENCODE(deltaA); 296 changes |= NEW_A; 297 } 298 299 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 300 if (deltaS) { 301 if (deltaS > 0xffff) 302 goto uncompressed; 303 ENCODE(deltaS); 304 changes |= NEW_S; 305 } 306 307 switch(changes) { 308 case 0: 309 /* 310 * Nothing changed. If this packet contains data and the 311 * last one didn't, this is probably a data packet following 312 * an ack (normal on an interactive connection) and we send 313 * it compressed. Otherwise it's probably a retransmit, 314 * retransmitted ack or window probe. Send it uncompressed 315 * in case the other side missed the compressed version. 316 */ 317 if (ip->ip_len != cs->cs_ip.ip_len && 318 ntohs(cs->cs_ip.ip_len) == hlen) 319 break; 320 321 /* FALLTHROUGH */ 322 323 case SPECIAL_I: 324 case SPECIAL_D: 325 /* 326 * actual changes match one of our special case encodings -- 327 * send packet uncompressed. 328 */ 329 goto uncompressed; 330 331 case NEW_S|NEW_A: 332 if (deltaS == deltaA && 333 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 334 /* special case for echoed terminal traffic */ 335 changes = SPECIAL_I; 336 cp = new_seq; 337 } 338 break; 339 340 case NEW_S: 341 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 342 /* special case for data xfer */ 343 changes = SPECIAL_D; 344 cp = new_seq; 345 } 346 break; 347 } 348 349 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 350 if (deltaS != 1) { 351 ENCODEZ(deltaS); 352 changes |= NEW_I; 353 } 354 if (th->th_flags & TH_PUSH) 355 changes |= TCP_PUSH_BIT; 356 /* 357 * Grab the cksum before we overwrite it below. Then update our 358 * state with this packet's header. 359 */ 360 deltaA = ntohs(th->th_sum); 361 BCOPY(ip, &cs->cs_ip, hlen); 362 363 /* 364 * We want to use the original packet as our compressed packet. 365 * (cp - new_seq) is the number of bytes we need for compressed 366 * sequence numbers. In addition we need one byte for the change 367 * mask, one for the connection id and two for the tcp checksum. 368 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 369 * many bytes of the original packet to toss so subtract the two to 370 * get the new packet size. 371 */ 372 deltaS = cp - new_seq; 373 cp = (u_char *)ip; 374 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 375 comp->last_xmit = cs->cs_id; 376 hlen -= deltaS + 4; 377 cp += hlen; 378 *cp++ = changes | NEW_C; 379 *cp++ = cs->cs_id; 380 } else { 381 hlen -= deltaS + 3; 382 cp += hlen; 383 *cp++ = changes; 384 } 385 m->m_len -= hlen; 386 m->m_data += hlen; 387 *cp++ = deltaA >> 8; 388 *cp++ = deltaA; 389 BCOPY(new_seq, cp, deltaS); 390 INCR(sls_compressed) 391 return (TYPE_COMPRESSED_TCP); 392 393 /* 394 * Update connection state cs & send uncompressed packet ('uncompressed' 395 * means a regular ip/tcp packet but with the 'conversation id' we hope 396 * to use on future compressed packets in the protocol field). 397 */ 398 uncompressed: 399 BCOPY(ip, &cs->cs_ip, hlen); 400 ip->ip_p = cs->cs_id; 401 comp->last_xmit = cs->cs_id; 402 return (TYPE_UNCOMPRESSED_TCP); 403 } 404 405 int 406 sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp) 407 { 408 u_char *hdr, *cp; 409 int hlen, vjlen; 410 411 cp = bufp? *bufp: NULL; 412 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 413 if (vjlen < 0) 414 return (0); /* error */ 415 if (vjlen == 0) 416 return (len); /* was uncompressed already */ 417 418 cp += vjlen; 419 len -= vjlen; 420 421 /* 422 * At this point, cp points to the first byte of data in the 423 * packet. If we're not aligned on a 4-byte boundary, copy the 424 * data down so the ip & tcp headers will be aligned. Then back up 425 * cp by the tcp/ip header length to make room for the reconstructed 426 * header (we assume the packet we were handed has enough space to 427 * prepend 128 bytes of header). 428 */ 429 if ((intptr_t)cp & 3) { 430 if (len > 0) 431 BCOPY(cp, ((intptr_t)cp &~ 3), len); 432 cp = (u_char *)((intptr_t)cp &~ 3); 433 } 434 cp -= hlen; 435 len += hlen; 436 BCOPY(hdr, cp, hlen); 437 438 *bufp = cp; 439 return (len); 440 } 441 442 /* 443 * Uncompress a packet of total length total_len. The first buflen 444 * bytes are at buf; this must include the entire (compressed or 445 * uncompressed) TCP/IP header. This procedure returns the length 446 * of the VJ header, with a pointer to the uncompressed IP header 447 * in *hdrp and its length in *hlenp. 448 */ 449 int 450 sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type, 451 struct slcompress *comp, u_char **hdrp, u_int *hlenp) 452 { 453 u_char *cp; 454 u_int hlen, changes; 455 struct tcphdr *th; 456 struct cstate *cs; 457 struct ip *ip; 458 u_int16_t *bp; 459 u_int vjlen; 460 461 switch (type) { 462 case TYPE_UNCOMPRESSED_TCP: 463 ip = (struct ip *) buf; 464 if (ip->ip_p >= MAX_STATES) 465 goto bad; 466 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 467 comp->flags &=~ SLF_TOSS; 468 ip->ip_p = IPPROTO_TCP; 469 /* 470 * Calculate the size of the TCP/IP header and make sure that 471 * we don't overflow the space we have available for it. 472 */ 473 hlen = ip->ip_hl << 2; 474 if (hlen + sizeof(struct tcphdr) > buflen) 475 goto bad; 476 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2; 477 if (hlen > MAX_HDR || hlen > buflen) 478 goto bad; 479 BCOPY(ip, &cs->cs_ip, hlen); 480 cs->cs_hlen = hlen; 481 INCR(sls_uncompressedin) 482 *hdrp = (u_char *) &cs->cs_ip; 483 *hlenp = hlen; 484 return (0); 485 486 default: 487 goto bad; 488 489 case TYPE_COMPRESSED_TCP: 490 break; 491 } 492 /* We've got a compressed packet. */ 493 INCR(sls_compressedin) 494 cp = buf; 495 changes = *cp++; 496 if (changes & NEW_C) { 497 /* Make sure the state index is in range, then grab the state. 498 * If we have a good state index, clear the 'discard' flag. */ 499 if (*cp >= MAX_STATES) 500 goto bad; 501 502 comp->flags &=~ SLF_TOSS; 503 comp->last_recv = *cp++; 504 } else { 505 /* this packet has an implicit state index. If we've 506 * had a line error since the last time we got an 507 * explicit state index, we have to toss the packet. */ 508 if (comp->flags & SLF_TOSS) { 509 INCR(sls_tossed) 510 return (-1); 511 } 512 } 513 cs = &comp->rstate[comp->last_recv]; 514 hlen = cs->cs_ip.ip_hl << 2; 515 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 516 th->th_sum = htons((*cp << 8) | cp[1]); 517 cp += 2; 518 if (changes & TCP_PUSH_BIT) 519 th->th_flags |= TH_PUSH; 520 else 521 th->th_flags &=~ TH_PUSH; 522 523 switch (changes & SPECIALS_MASK) { 524 case SPECIAL_I: 525 { 526 u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 527 th->th_ack = htonl(ntohl(th->th_ack) + i); 528 th->th_seq = htonl(ntohl(th->th_seq) + i); 529 } 530 break; 531 532 case SPECIAL_D: 533 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 534 - cs->cs_hlen); 535 break; 536 537 default: 538 if (changes & NEW_U) { 539 th->th_flags |= TH_URG; 540 DECODEU(th->th_urp) 541 } else 542 th->th_flags &=~ TH_URG; 543 if (changes & NEW_W) 544 DECODES(th->th_win) 545 if (changes & NEW_A) 546 DECODEL(th->th_ack) 547 if (changes & NEW_S) 548 DECODEL(th->th_seq) 549 break; 550 } 551 if (changes & NEW_I) { 552 DECODES(cs->cs_ip.ip_id) 553 } else 554 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 555 556 /* 557 * At this point, cp points to the first byte of data in the 558 * packet. Fill in the IP total length and update the IP 559 * header checksum. 560 */ 561 vjlen = cp - buf; 562 buflen -= vjlen; 563 if (buflen < 0) 564 /* we must have dropped some characters (crc should detect 565 * this but the old slip framing won't) */ 566 goto bad; 567 568 total_len += cs->cs_hlen - vjlen; 569 cs->cs_ip.ip_len = htons(total_len); 570 571 /* recompute the ip header checksum */ 572 bp = (u_int16_t *) &cs->cs_ip; 573 cs->cs_ip.ip_sum = 0; 574 for (changes = 0; hlen > 0; hlen -= 2) 575 changes += *bp++; 576 changes = (changes & 0xffff) + (changes >> 16); 577 changes = (changes & 0xffff) + (changes >> 16); 578 cs->cs_ip.ip_sum = ~ changes; 579 580 *hdrp = (u_char *) &cs->cs_ip; 581 *hlenp = cs->cs_hlen; 582 return vjlen; 583 584 bad: 585 comp->flags |= SLF_TOSS; 586 INCR(sls_errorin) 587 return (-1); 588 } 589